From Sonic Retro
The Light Dash, also known as the Light Speed Dash or the Lightspeed Dash, is a technique that can only be used by Sonic the Hedgehog and Shadow the Hedgehog. The move allows the user to cross a trail of rings.
The Light Dash first debuted in Sonic Adventure, but it was known as the "Light Speed Dash". The Light Speed Shoes are required to use this technique. The move was pretty inconvenient to use at the time as Sonic had to spin charge in order to use it. But getting the Crystal Ring will shorten the time needed to charge for the move.
Sonic Adventure 2
In Sonic Adventure 2, the Light Dash was made slightly easier to use. After obtaining the Light Shoes (Sonic) or Air Shoes (Shadow), the player can cross a trail of rings by approaching them and pressing the button. The Crystal Ring has been removed because of this.
The Light Dash made another appearance in Sonic Heroes. It functions the exact same was as it did in Sonic Adventure 2. Again, only Sonic and Shadow are capable of using the technique, meaning Team Sonic and Team Dark are the only teams that can use it. Though, Shadow's is known as Dark Dash. Because there are no upgrades in this game, Sonic and Shadow can use the Light Dash by default.
The Light Dash returns in Sonic Unleashed. In the PS2 and Wii versions, it can be used by default. However, in the PS3 and Xbox 360 versions of the game, the player must obtain the Light Shoes from the Shamar hub area. Unlike previous appearances of the Light Dash, it has been given its own seperate button.
The Light Dash returns once again in Sonic Generations. The Light Dash controls much like it did in Sonic Unleashed: The player can use it through certain ring paths only. The Light Dash is also a default move from the beginning, with no known upgrades for it. However, the move can only be used on certain lines of illuminated rings.
In Sonic Forces, the Light Dash can be used by the Avatar, but only if they obtain an Ivory Wisp while using a Lightning Wispon. While the Wispon's special action is in use, the Avatar can travel along ring paths.
In other media
While there was no actual Light Dash in Sonic X, there was something similar known as the Ring Road. It was invented by Chris Thorndyke. If he stocked rings inside his plane's ammunition chamber, he can fire the rings out and make them form a ring tunnel. Sonic can zip through this tunnel and attack the enemies.